The present invention relates generally to separation of fetal erythrocytes from maternal blood samples. More particularly, the present invention provides a system and non-invasive method for enriching the population of nucleated fetal erythrocytes or nucleated fetal red blood cells ("NRBCs") obtained from maternal blood samples by separating the NRBCs from the mother's erythrocytes, leukocytes and other blood components. More specifically, the present invention offers a system and method for enriching the population of NRBCs from a maternal blood sample which concentrates the NRBCs by electrophoresis and/or adsorption-filtration or affinity filtration.
Physicians have long sought to develop non-invasive methods for prenatal diagnosis because the available methods, amniocentesis and chorionic villus sampling (CVS) are potentially harmful to the mother and to the fetus. The rate of miscarriage for pregnant women undergoing amniocentesis is increased by 0.5-1%, and that figure is be slightly higher for CVS. Because of the inherent risks posed by amniocentesis and CVS, these procedures are offered primarily to older women, i.e., those over 35 years of age, who have a statistically greater probability of bearing children with congenital defects.
Some non-invasive methods have already been developed to diagnose specific congenital defects. For example, maternal serum alpha-fetoprotein, and levels of unconjugated estriol and human chorionic gonadotropin can be used to identify a proportion of fetuses with Downs syndrome. Similarly, ultrasonography is used to determine congenital defects involving neural tube defects and limb abnormalities.
Separation of nucleated fetal erythrocytes from maternal blood has been proposed as a viable method for facilitating prenatal diagnosis of genetic disorders. Fetal NRBCs have been separated from maternal blood by flow cytometry using a lysing reagent (European Published Patent Application No. 582736, published Feb. 16, 1994); by triple gradient discontinuous gradient gel electrophoresis (Bhat, et al, U.S. Pat. No. 5,275,933, issued Jan. 4, 1994); by separation from nucleated cells using leukocyte depletion and lysis of non-nucleated erythrocytes using ammonium chloride (Goldbard, PCT Publication WO 9417209, published Aug. 4, 1994); by use of anti-CD71 monoclonal antibody and magnetic beads and in-situ fluorescence hybridization (FISH) (Ahlert, et al, German Published Patent Application No. 4222573, published Aug. 12, 1993) or by other antibodies specific to a fetal erythrocyte antigen (Bianchi, PCT Publication WO 9107660, published May 30, 1991).